ORIGIN OF STASSFURT SALTS 375 



parently much as they are to-day. As a result, rainy conditions 

 prevailed on the windward side of these mountains, where the old 

 mediterranean or Thetis Sea of that day was situated, but arid 

 conditions were produced over the region beyond these mountains 

 by these winds, which on crossing the mountains became aridifiers. 

 As a result of this change in climate the region of North Germany, 

 Belgium, etc., previously one of much moisture and characterized 

 by the formation of luxurious coal swamps, became the theatre of 

 deposition of the red sands of the low^er Permic or Rothliegende. 

 The lower division of this deposit forms a transition from the coal- 

 bearing formations preceding and contains at first some coal and 

 plant remains. Extensive forests of calamites, ferns, and conifers 

 covered the rising lands, for at first the barrier was not sufficient to 

 keep the moist wands out. The progressive development of the 

 mountain system finally involved some of the earlier Rothliegende 

 deposits, so that the later division, mostly free from plant remains, 

 rests unconformably. in part on the folded and eroded lower divi- 

 sion. There is thus indicated a progressive aridification of the 

 region, due no doubt to the continued growth of the Armorican 

 Mountain system which became more and more effective as a bar- 

 rier for the moisture-laden southwest winds. 



The Rothliegende desert was invaded by the Zechstein Sea from 

 the North Russia region, marked at first by invading channels with 

 a marine fauna, wdiile elsewhere sand-dunes, now forming the 

 Weissliegende, covered the lowlands. Then followed the pectiliar 

 conditions producing the Kupferschiefer, which were probably due 

 to a separation of the early waters from the ocean to the north, to 

 form a shallow, brackish lake into which streams from the sur- 

 rounding old land, the Harz, Frankenwald, Erzgebirge, and rhein- 

 ische Schiefergebirge, carried mineral matter in solution. The abun- 

 dant fish fauna of this lake eventually succumbed to the gradual 

 fotiling of these stagnant waters and the carcasses were buried in 

 the black muds, which also enclosed the metallic precipitates. The 

 renewed invasion of this area by the Russian Sea then led to the 

 formation of the marine Zechstein with its Bryozoa reefs and rich 

 fauna, and for a long time the conditions of an open sea existed 

 over North Europe. That the winds from the southwest still main- 

 tained their drying. characteristic is shown by the deposits of western 

 England, which remained of the arid type, and extended down to, 

 and perhaps partly into, the Zechstein (Magnesian limestone) Sea. 

 The marine fauna of the Zechstein found conditions of existence 

 more favorable where the old Kupferschiefer muds were absent, as 

 around the margins of the old lands and the projecting islands of 



